Hi Naoya, On Mon, Aug 26, 2013 at 08:12:29PM -0400, Naoya Horiguchi wrote: >Hi Wanpeng, > >On Tue, Aug 27, 2013 at 07:26:04AM +0800, Wanpeng Li wrote: >> Hi Naoya, >> On Mon, Aug 26, 2013 at 11:45:37AM -0400, Naoya Horiguchi wrote: >> >On Mon, Aug 26, 2013 at 04:46:12PM +0800, Wanpeng Li wrote: >> >> madvise hwpoison inject will poison the read-only empty zero page if there is >> >> no write access before poison. Empty zero page reference count will be increased >> >> for hwpoison, subsequent poison zero page will return directly since page has >> >> already been set PG_hwpoison, however, page reference count is still increased >> >> by get_user_pages_fast. The unpoison process will unpoison the empty zero page >> >> and decrease the reference count successfully for the fist time, however, >> >> subsequent unpoison empty zero page will return directly since page has already >> >> been unpoisoned and without decrease the page reference count of empty zero page. >> >> This patch fix it by decrease page reference count for empty zero page which has >> >> already been unpoisoned and page count > 1. >> > >> >I guess that fixing on the madvise side looks reasonable to me, because this >> >refcount mismatch happens only when we poison with madvise(). The root cause >> >is that we can get refcount multiple times on a page, even if memory_failure() >> >or soft_offline_page() can do its work only once. >> > >> >> I think this just happen in read-only before poison case against empty >> zero page. > >OK. I agree. > >> Hi Andrew, >> >> I see you have already merged the patch, which method you prefer? >> >> >How about making madvise_hwpoison() put a page and return immediately >> >(without calling memory_failure() or soft_offline_page()) when the page >> >is already hwpoisoned? >> >I hope it also helps us avoid meaningless printk flood. >> > >> >> Btw, Naoya, how about patch 10/10, any input are welcome! ;-) > >No objection if you (and Andrew) decide to go with current approach. Andrew prefer your method, I will resend the patch w/ your suggested-by. ;-) >But I think that if we shift to fix this problem in madvise(), >we don't need 10/10 any more. So it looks simpler to me. I don't think it's same issue. There is just one page in my test case. #define PAGES_TO_TEST 1 If I miss something? Regards, Wanpeng Li > >Thanks, >Naoya Horiguchi -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>